The present invention relates to a semiconductor device, and more particularly to techniques which are effective when applied to a semiconductor device having a plurality of leads that extend inside and outside a sealing body.
A semiconductor device of QFP (Quad Flat Package) type, for example, has been known as one of semiconductor devices well suited for increasing the number of pins. In general, the semiconductor device of the QFP type is manufactured by an assembling process employing a lead frame. Concretely, it is manufactured in such a way that a semiconductor chip is mounted through an adhesive on the chip mounting surface of a die pad (also termed a xe2x80x9ctabxe2x80x9d) which is supported on the frame member of the lead frame through supporting leads, that electrodes (also termed xe2x80x9cbonding padsxe2x80x9d) formed on the circuit forming surface of the semiconductor chip and the inner lead portions (also termed the xe2x80x9cinner leadsxe2x80x9d) of leads (leads for connections) supported by the frame member of the lead frame are thereafter electrically connected by pieces of conductive wire, that the semiconductor chip, the die pad, the supporting leads, the inner lead portions of the connection leads, and the wire pieces are thereafter encapsulated with a sealing body which is made of an insulating resin, that tie bars (also termed xe2x80x9cdam barsxe2x80x9d) which tie the adjacent ones of the connection leads are thereafter cut away, that the outer lead portions (also termed the xe2x80x9couter leadsxe2x80x9d) of the connection leads are thereafter subjected to a plating treatment, that the outer lead portions of the connection leads are thereafter cut away from the frame member of the lead frame, that the outer lead portions of the connection leads are thereafter shaped into a gull-wing shape which is one of flat packaging (surface-mounted) lead shapes, and that the supporting leads are thereafter cut away from the frame member of the lead frame.
Each of the outer lead portions of the connection leads molded into the gull-wing shape is constructed having a root part which protrudes out of the sealing body, an intermediate part which bends downwards from the root part, and a mounting part which extends from the intermediate part in the same direction as the extending direction of the root part. Such mounting parts are employed as terminal parts for external connections in the case where the semiconductor device is soldered and mounted onto a mounting substrate.
Meanwhile, in the semiconductor device of the QFP type, the number of pins is increasing more and more as a circuit system to be included in the semiconductor chip becomes higher in the density of integration and larger in the number of functions. A lead array in the outer lead portions of the connection leads is set at a narrower pitch with the increase in the number of pins.
The narrower pitch of the outer lead portions is promoted by narrowing the interval between the adjacent connection leads and the width of each of the connection leads. Therefore, when the semiconductor device is soldered and mounted onto the mounting substrate, such defective mounting is liable to occur that a solder bridge appears across the mounting parts of a certain one of the outer lead portions and the outer lead portion adjoining the certain outer lead portion, to short-circuit the corresponding adjacent leads.
Besides, when the outer lead portions are molded into the gull-wing shape, such defective lead molding is liable to occur that the outer lead portions are molded into a state where they bend in the direction of arraying the connection leads (laterally of the outer lead portions), due to their insufficient mechanical strength. The defective lead molding forms a factor for incurring the short-circuit defect that the mounting part of a certain one of the outer lead portions comes into touch with the mounting part of the outer lead portion adjoining the certain outer lead portion, and also a factor for incurring the appearance of the solder bridge in the mounting operation.
As a technique for solving such problems ascribable to the narrowed pitch of the outer lead portions, by way of example, one wherein the lead width of the shoulder part (root part) of the outer lead of each connection lead is set broader than that of the base part (mounting part) thereof is disclosed in the official gazette of Japanese Patent Laid-open No. 350003/1994 (laid open on Dec. 22, 1994). According to this technique, the shoulder parts of the outer leads are endowed with sufficient rigidity. Therefore, even when mechanical stresses have acted on the shoulder parts in the forming operation, the connection leads do not deform into greatly discrepant geometries, so that a conduction defect ascribable to the touch between the connection leads adjoining each other, a conduction defect ascribable to the insufficient touch of the connection lead with an electrode, etc. can be prevented from occurring. Moreover, a pitch of predetermined dimension is ensured by narrowing the lead width of the base parts of the outer leads. Therefore, in a case where a semiconductor integrated circuit device is soldered to a printed circuit board, the solder bridge due to which the adjacent connection leads are electrically connected by a solder can be simultaneously prevented from appearing.
A point to be explained below, however, is not considered in the technique mentioned above.
The bend of the outer lead portions in the connection lead arraying direction in the forming operation is governed by the lead width of the root parts of the outer lead portions. In a case where the lead width of the root parts is equal to or greater than the lead thickness thereof, the mechanical strength of the root parts in the connection lead arraying direction is high, and hence, the bend of the outer lead portions in the connection lead arraying direction in the forming operation can be suppressed to some extent. However, in a case where the lead width of the root parts is less than the lead thickness thereof, the mechanical strength of the root parts in the connection lead arraying direction is low, and hence, the bend of the outer lead portions in the connection lead arraying direction in the forming operation becomes difficult of suppression. In other words, the lead thickness of the root parts needs to be considered in order that the defective lead forming of the outer lead portions may be suppressed by setting the lead width of the root parts broader than the lead width of the mounting parts.
An object of the present invention is to provide techniques which are capable of suppressing the defective lead forming and defective mounting of a semiconductor device.
The above and other objects and novel features of the present invention will become apparent from the description of this specification when read in conjunction with the accompanying drawings.
A typical aspect of performance of the present invention is briefly summarized as follows:
A semiconductor device comprises a sealing body which has a square planar shape, a semiconductor chip which lies within said sealing body, and a plurality of leads (leads for connections) which are electrically connected with electrodes of said semiconductor chip, which extend inside and outside said sealing body and which are arrayed along latera of said sealing body, wherein an outer lead portion of each of said leads is such that a root part which protrudes out of said sealing body is formed at a lead width being equal to or greater than a lead thickness, and that a mounting part which joins to said root part through an intermediate part is formed at a lead width being less than the lead thickness.
According to the above expedient, the root parts of the outer lead portions are formed at the lead width equal to or greater than the lead thickness, so that the mechanical strength of the root parts in the direction of arraying the leads becomes higher than in case of forming the root parts of the outer lead portions at a lead width less than the lead thickness. It is therefore possible to suppress the defective lead forming that, in a lead forming operation for the outer lead portions, these outer lead portions are shaped into a state where they bend in the lead arraying direction.
Besides, the mounting parts of the outer lead portions are formed at the lead width less than the lead thickness, so that the interval between the respectively adjacent leads at the mounting parts becomes broader than in case of forming the mounting parts of the outer lead portions at a lead width equal to or greater than the lead thickness. It is therefore possible to suppress solder bridges which appear across the mounting parts of the adjacent leads in soldering and mounting the semiconductor device onto a mounting substrate, and to suppress the defective mounting that the adjacent leads short-circuit.